British Calves Research Articles

Metabolic changes in cattle due to the specific effect of the tick, Boophilus microplus.

1. An experiment was designed to provide information on the alterations in body metabolism which would account for the loss of body-weight in cattle due to the specific effect (factors other than reduced food intake) of the tick Boophilus microplus. 2. Two groups of British (Shorthorn x Hereford) and Africander x British calves, each approximately months olds, were used: one group (treated) of each breed was tick-infested and the other (control) was tick-free. Within breeds, calves in the control group were pair-fed to calves in the treated group. 3. In both breeds, the effect of ticks: (a) depressed packed cell volume, serum alkaline phosphatase (EC 3.1.3.1) and amylase (EC 3.2.1.1.) activities, plasma cholesterol and phospholipid levels, serum iron and albumin levels, (b) increased the plasma levels of urea-nitrogen and gamma-globulin (c) increased rectal temperature, water intake, urine volume, urinary and faecal total N, urinary urea-N and alpha-amino acids, the excretion of water, sodium and potassium in the faeces and (d) reduced N balance, N and dry-matter digestibilities. 4. In the British breed, ticks increased the excretion of K with a corresponding decrease in the excretion of Na in the urine and increased the plasma clearance of bromsulphthalein. 5. A second experiment showed that the specific effect of tick infestation increased the flow of organic matter (OM) from the abomasum and the fractional turnover of rumen fluid of Hereford steers. It was also shown that the decrease in OM digestibility in the gastrointestinal tract was largely due to a decrease in OM digestibility in the rumen and that the increased urinary urea excretion and plasma urea concentration was caused by higher production rates of urea despite a tendency for lowered urea degradation in the gastrointestinal tract.

Resistance to Boophilus microplus (Canestrini) in Genetically Different Types of Calves in Early Life

Tick resistance and blood composition were studied in British (1/2 Shorthorn x 1/2 Hereford) and zebu (1/2 Brahman x 1/2 British) calves from birth to 33 days of age in a tropical grazing area in which B. microplus is endemic. Calves of the 2 breeds were either naturally infested or were, in addition, artificially infested with 5,000 larvae at 2 and 9 days of age. Total numbers of mature female ticks carried from either type of infestation were significantly lower (P less than 0.01) on zebu than on British calves. In the artificially infested calves of both breeds, the total number of ticks maturing between 20 to 26 days of age was significantly higher (P less than 0.01) than the number maturing between 27 to 33 days of age emphasizing that a major component of resistance is acquired. However, in the naturally infested calves, breed differences in the numbers of ticks maturing during these 2 periods suggested the presence of genetic differences in innate resistance. Within breeds, total tick numbers carried during the study were negatively correlated with calf weight gain and with the concentrations of serum albumin, total protein, and cholesterol.

Changes in lipid metabolism in genetically different types of calves during chronic hyperthermia.

1. The effects of chronically raised body temperature on lipid metabolism were studied in groups of 3-month-old British (Shorthorn × Hereford) and Zebu (Africander × British) bull calves. Calves in control groups at ambient temperature were pair-fed to calves housed in a climate room.2. In control groups, concentrations of plasma cholesterol and phospholipid were significantly higher and the excretion of fatty acids 14:0, 16:0 and 18:0 was lower in the Zebu than in the British calves.3. In the climate room the constant daily environmental temperature required to maintain an increase in rectal temperature of 1·3° was 33° for British and 38° for Zebu calves. Changes in respiration rate, water metabolism and nitrogen metabolism associated with hyperthermia were similar in both breeds.4. Hyperthermia in all animals was associated with lowered plasma concentrations of cholesterol and phospholipid and increases in the ratio of free to total cholesterol. It was without effect on the circulating concentrations of non-esterified fatty acids and about twice the amount of fat was excreted without change in its fatty acid composition.5. The results showed that, when control of normal body temperature was lost, increased rectal temperature led to similar metabolic changes in animals of both breeds.